Housing Fastening Method

ABSTRACT

An object of the present invention is to provide, by contriving a housing structure, a housing fastening method and turbocharger capable of keeping down a reduction in fastening force applied by a G-coupling even when housings are exposed to high temperature. 
     The present invention provides a turbocharger comprising a turbine  1  including a bladed rotor  1   a  rotated by a fluid supplied thereto, a compressor  2  including an impeller  2   a  for drawing in air, connected with the bladed rotor  1   a  by a rotating shaft  3   a , a turbine housing  1   b  constituting an outer shape of the turbine  1 , and a bearing housing  3  rotatably supporting the rotating shaft  3   a , a projecting portion  3   b  of the bearing housing  3  being inserted in a recessed portion  1   c  of the turbine housing  1   b  such that an end face  3   c  of the projecting portion  3   b  butts against a step portion  1   d  of the recessed portion  1   c  serving as a stopper face, a flange portion  1   e  around the recessed portion  1   c  and a flange portion  3   d  around the projecting portion  3   b  being fastened together by an annular fastener positioned outside, wherein the shapes of the recessed portion  1   c  and the projecting portion  3   b  are determined by regulating the axial position of the stopper face of the step portion  1   d.

TECHNICAL FIELD

This invention relates to a housing fastening method for fasteninghousings together by a fastener such as a G-coupling and a turbochargerhaving housings fastened together by a fastener such as a G-coupling,and particularly a housing fastening method and turbocharger capable ofkeeping down a reduction in fastening force applied by a fastener.

BACKGROUND ART

A rotary machine which obtains power by converting kinetic energy of afluid supplied to its bladed rotor to rotation of the bladed rotor isgenerally called a turbine. A type in which a fluid is supplied to thebladed rotor radially and discharged axially is called a radial turbine,in particular. An automotive turbocharger is a device using such radialturbine. The automotive turbocharger comprises a gas turbine including abladed turbine rotor rotated by exhaust gas supplied thereto and acompressor including an impeller for drawing in air, connected with thebladed turbine rotor coaxially. The air drawn in and compressed by thecompressor is delivered to an engine, where it is mixed with fuel andburnt. Exhaust gas produced from combustion is sent to the gas turbineto do work, and finally emitted into the atmosphere. The passage throughwhich the exhaust gas is supplied to the bladed turbine rotor includes ascroll portion extending spirally around the axis of rotation of thebladed turbine rotor so that the exhaust gas is accelerated and suppliedto the bladed turbine rotor radially.

The automotive turbocharger as described above has a rotating shaftwhich connects the bladed turbine rotor of the gas turbine and theimpeller of the compressor. The rotating shaft is supported by a bearinghousing, rotatably. In some cases, a turbine housing and the bearinghousing are connected together by fastening a fastener such as aG-coupling to flange portions of the turbine housing and bearing housing(see Patent Document 1, FIG. 12, for example).

Patent Document 1: Japanese Patent Application KOKAI Publication2006-258108, FIG. 12

When the turbine housing and the bearing housing are fastened togetherby a fastener such as a G-coupling as in Patent Document 1, however,thermal expansion of the flange portions and fastener during use of theturbocharger sometimes produces a gap between the flange portions andthe fastener due to difference in linear coefficient of expansionbetween the respective flange portions and the fastener, which resultsin a reduction in fastening force applied by the fastener. Further,exposure of the turbine housing inside to high-temperature exhaust gascauses thermal expansion of its flange portion, which in turn causesdeformation of the fastener. This sometimes results in a reduction infastening force applied by the fastener when the exhaust gas temperaturedrops.

DISCLOSURE OF THE INVENTION

The present invention has been made to solve the problems as mentionedabove. An object of the present invention is to provide, by contriving ahousing structure, a housing fastening method and turbocharger capableof keeping down the reduction in fastening force applied by a fastenersuch as a G-coupling even when housings are exposed to high temperature.

In order to achieve the above object, the present invention provides ahousing fastening method comprising the steps of inserting a projectingportion of a housing in a recessed portion of another housing so that anend face of the projecting portion butts against a step portion of therecessed portion serving as a stopper face and that a flange portionaround the recessed portion and a flange portion around the projectingportion face each other, and thereafter, fastening the housings togetherby an annular fastener with a grooved portion on its inside adapted toreceive the flange portions facing each other, wherein the axialposition of the stopper face of the step portion and the shapes of therecessed portion and the projecting portion are determined to ensurethat a gap produced between the grooved portion of the fastener and theflange portions does not exceed a specified size even when the housingsand the fastener experience thermal expansion during use.

The above-described housing fastening method according to the presentinvention was contrived through the inventor's keen research onreduction in fastening force applied by a fastener such as a G-couplingfor fastening housings together, due to thermal expansion, whichresearch led to the finding that there exists a connection between theaxial position of the stopper face of the step portion and the fasteningforce applied by the fastener. This means that by regulating the axialposition of the stopper face of the step portion, reduction in fasteningforce applied by the fastener can be kept down, without requiring fulldiscovery of thermal expansion of the flange portions and fastener.Consequently, even under thermal expansion, the gap produced between thefastener and the flange portions can be easily controlled byappropriately determining the axial position of the stopper face of thestep portion and the shapes of the recessed portion and the projectingportion. For example, by setting the axial position of the stopper faceof the step portion nearer to the end (reducing the depth of therecessed portion) compared with the prior art, reduction in fasteningforce applied by the fastener due to thermal expansion can be kept downeven when the inside of the housing is exposed to high temperature (ca1000° C., for example).

In a preferred aspect of this housing fastening method, the axialposition of the stopper face of the step portion is set within the axialprojected width of the fastener.

This leads to a reduced axial distance between a contact position on thehousing having the recessed portion against the fastener and the stopperface of the step portion. Consequently, the reduction in fastening forceapplied by the fastener due to thermal expansion can be kept down, evenwhen the housing having the recessed portion is exposed to highertemperature compared with the housing having the projecting portion andthe fastener, in particular.

Specifically, the axial distance between the contact positions on therespective flange portions against the fastener is equal to the axialdistance between the stopper face and the contact position on the flangeportion of the housing having the recessed portion against the fastenersubtracted from the axial distance between the stopper face and thecontact position on the flange portion of the housing having theprojecting portion against the fastener. Theoretically, as long as thehousings and the fastener experience uniform thermal expansion, thereoccurs no reduction in fastening force applied by the fastener. If,however, the housing having the recessed portion experiences a greaterdegree of thermal expansion compared with the housing having theprojecting portion, the axial distance between the contact positions onthe respective flange portions against the fastener relatively reduces,so that a gap is produced between the housings and the fastener.

In the preferred aspect, however, since the axial distance between thecontact position on the flange portion of the housing having therecessed portion against the fastener and the stopper face of the stepportion is small, the increase in the axial distance between the contactposition and the stopper face due to thermal expansion of the housinghaving the recessed portion is very small. Consequently, even when thehousing having the recessed portion is exposed to higher temperaturecompared with the housing having the projecting portion and thefastener, increase in size of the gap between the housings and thefastener due to thermal expansion can be kept down, so that reduction infastening force applied by the fastener can be kept down.

In another aspect of the housing fastening method according to thepresent invention, the shape of the projecting portion is determinedtaking account of the thickness of a thin sheet held between the stopperface of the step portion and the end face of the projecting portion.

In this aspect, when a thin sheet, such as a spacer or a heat shieldplate, is provided between the stopper face of the step portion of oneof the adjoining housings and the end face of the projecting portion ofthe other housing, thermal expansion of this thin sheet is also takeninto consideration, so that the reduction in fastening force applied bythe fastener due to thermal expansion can be more effectively kept down.

In another aspect of the housing fastening method according to thepresent invention, the flange portion of the housing which is likely toexperience a smaller degree of thermal expansion is formed to be greaterin outside diameter than the flange portion of the housing which islikely to experience a greater degree of thermal expansion.

This aspect enables the edges of both flange portions to takeapproximately the same radial position at high temperature, although thehousings fastened together experience different degrees of thermalexpansion, thereby greatly reducing a force tending to tilt thefastener.

In a specific aspect, the axial distance Az from the contact position atwhich the fastener contacts the flange portion around the recessedportion to the stopper face of the step portion and the axial distanceBz from the contact position at which the fastener contacts the flangeportion around the projecting portion to the end face of the projectingportion are determined to meet the condition 0≦Cg−C≦allowable limit k,where C is an axial distance between the contact positions on the flangeportions defined by an expression C=t+Bz−Az, on the basis of said axialdistances Az and Bz, and Cg is an axial distance between the contactpositions on the fastener. Here, the allowable limit k may be set on thebasis of the allowable size for a gap produced between the fastener andthe contact position on the flange portion at a specified temperature.Specifically, it is desirable to set the allowable limit k to meet thecondition 0≦k<0.0388/cos(θ/2), where θ is an angle of divergence of apair of support portions of the fastener.

In this specific aspect, determining the axial distance Az in therecessed portion and the axial distance Bz in the projecting portion tomeet the above-mentioned condition leads to limiting the size of the gapproduced between the fastener and the flange portion at high temperaturewithin a desired range. Consequently, reduction in fastening forceapplied by the fastener can be kept down.

The present invention also provides a turbocharger comprising a turbineincluding a bladed rotor rotated by a fluid supplied thereto, acompressor including an impeller for drawing in air, connected with thebladed rotor by a rotating shaft, a turbine housing constituting anouter shape of the turbine, and a bearing housing rotatably supportingthe rotating shaft, a projecting portion of the bearing housing beinginserted in a recessed portion of the turbine housing such that an endface of the projecting portion butts against a step portion of therecessed portion serving as a stopper face and that a flange portionaround the recessed portion and a flange portion around the projectingportion face each other, the flange portions being fastened together byan annular fastener with a grooved portion on its inside adapted toreceive the flange portions facing each other, wherein the bearinghousing and the turbine housing are fastened together by the fasteneraccording to any of the above aspects of the housing fastening method.

The turbocharger having a configuration described above can keep downthe reduction in fastening force applied by the fastener due to thermalexpansion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a longitudinal cross-sectional view of a turbochargeraccording to the present invention.

FIG. 1B is a front view of a G-coupling 4 shown in FIG. 1A.

FIG. 2A is a diagram showing portion II of FIG. 1A on an enlarged scale.

FIG. 2B is a diagram showing a portion corresponding to the portionshown in FIG. 2A in prior art, on an enlarged scale.

FIG. 3 is an explanatory diagram indicating sizes referred to indescribing a housing fastening method according to an embodiment of thepresent invention.

FIG. 4A is a diagram showing a relation between a G-coupling 4 andflange portions 1 e and 3 d at normal temperature.

FIG. 4B is a diagram showing a relation between the G-coupling 4 and theflange portions 1 e and 3 d at high temperature.

FIG. 4C is a diagram showing a relation between gaps Δg and Δc shown inFIG. 4B.

FIG. 5A is a longitudinal cross-sectional view showing a fasteningstructure made by a housing fastening method according to anotherembodiment of the present invention.

FIG. 5B is a longitudinal cross-sectional view showing a fasteningstructure made by a housing fastening method according to anotherembodiment of the present invention.

BEST MODE OF CARRYING OUT THE INVENTION

Referring to FIGS. 1A to 5B, embodiments of the present invention willbe described below. FIG. 1A is a longitudinal cross-sectional view of aturbocharger according to the present invention, and FIG. 1B a frontview of a G-coupling shown in FIG. 1A. FIG. 2A shows portion II of FIG.1A on an enlarged scale, and FIG. 2B shows a portion corresponding tothe portion shown in FIG. 2A in prior art.

The turbocharger according to the present invention shown in FIG. 1Acomprises a turbine 1 including a bladed rotor la rotated by a fluidsupplied thereto, a compressor 2 including an impeller 2 a for drawingin air, connected with the bladed rotor 1 a by a rotating shaft 3 a, aturbine housing 1 b constituting an outer shape of the turbine 1, and abearing housing 3 rotatably supporting the rotating shaft 3 a. Theturbine housing 1 a and the bearing housing 3 and the bearing housing 3[sic] are assembled as follows: A projecting portion 3 b of the bearinghousing 3 is inserted in a recessed portion 1 c of the turbine housing 1a so that an end face 3 c of the projecting portion 3 b butts against astep portion 1 d of the recessed portion 1 c serving as a stopper faceand that a flange portion 1 e around the recessed portion 1 c and aflange portion 3 d around the projecting portion 3 b face each other.Then, the flange portions 1 e and 3 e are fastened together by anannular G-coupling 4 with a grooved portion on its inside adapted toreceive the flange portions 1 e and 3 d facing each other, where theaxial position of the stopper face of the step portion 1 d and theshapes of the recessed portion 1 c and the projecting portion 3 b aredetermined as described later. Incidentally, although the turbine 1 ofthe turbocharger shown in FIG. 1A has a multiple-chamber scroll portion1 f, the present invention is not limited to this configuration. Theturbocharger may have a single-chamber scroll portion, and may include avariable nozzle for regulating flow rate, between the scroll portion 1 fand the bladed rotor 1 a. Further, although in the drawing, a compressorhousing 2 b and the bearing housing 3 are fastened together by bolts 2 cdistributed circumferentially, they may be fastened together in anothermanner.

In the turbocharger shown in FIG. 1A, the axial position of the stopperface of the step portion 1 d is set, for example within the axialprojected width Zg of the G-coupling 4, as indicated in FIG. 2A. Here,if the flange portions 1 e and 3 d are approximately equal in axialwidth, there exists a relationship Za≦0.5Zg, where Za is the axialdistance between the end face of the flange portion 1 e and the stopperface of the step portion 1 d of the turbine housing 1 b. In the priorart shown in FIG. 2B, on the other hand, the axial position of thestopper face of the step portion 1 d is set outside the axial projectedwidth Zg of the G-coupling 4, so that there exists a relationshipZa>0.5Zg. In the structure shown in FIG. 2B, when the inside of theturbine housing 1 b is exposed to high temperature (ca 1000° C., forexample), thermal expansion of the respective members may produce a gapbetween the G-coupling 4 and the flange portion 3 d, thereby causing areduction in fastening force, or the flange portions 1 e, 3 d maystretch and deform the G-coupling 4. Through keen research, the inventorhas discovered that there is a connection between the axial position ofthe stopper face of the step portion 1 d and the fastening force appliedby the G-coupling 4. Thus, in the present invention, the axial positionof the stopper face of the step portion 1 d is set nearer to the endface of the flange portion 1 e compared with the prior art so as tosolve the above-mentioned problems. In other words, in the turbochargeraccording to the present invention, the recessed portion 1 c has areduced depth (=Za) compared with the prior art.

In this configuration, the axial distance from the contact position onthe flange portion 1 e of the turbine housing 1 b against the G-coupling4 to the stopper face of the step portion 1 d is reduced. Thus, evenwhen the turbine housing 1 b is exposed to higher temperature comparedwith the bearing housing 3 and the G-coupling 4, reduction in fasteningforce applied by the G-coupling 4 due to thermal expansion can be keptdown.

Specifically, since the axial distance between the contact position onthe flange portion 1 e of the turbine housing 1 b against the G-coupling4 and the stopper face of the step portion 1 d is small, increase in theaxial distance between the contact position and the stopper face due tothermal expansion of the turbine housing 1 b is very small. Thus, evenwhen the turbine housing 1 b is exposed to higher temperature comparedwith the bearing housing 3 and the G-coupling 4, increase in size of thegap produced between the housings and the fastener due to thermalexpansion can be kept to a minimum, so that reduction in fastening forceapplied by the G-coupling 4 can be kept down.

The G-coupling 4 is a type of fastener, and as shown in FIG. 1B,includes a pair of semicircular arc portions 4 a, 4 a, flange portions 4b, 4 b at an end of the respective semicircular arc portions 4 a,turned-back portions 4 c, 4 c at the opposite end of the respectivesemicircular arc portions 4 a, a fastener 4 d such as a bolt and nut forfastening the flange portions 4 b together, and a ring 4 e for bindingthe turned-back portions 4 c, 4 c. As seen from the cross-sectional viewshown in FIG. 2A, each semicircular arc portion 4 a has the groovedportion adapted to receive the flange portion 1 e of the turbine housing1 b and the flange portion 3 d of the bearing housing 3, inside.

The grooved portion has sloping sides gradually diverging from eachother from the bottom to the top of the grooved portion. The flangeportion 1 a of the turbine housing 1 b and the flange portion 3 d of thebearing housing 3 each taper such that the flange portion can contactthe corresponding sloping surface of the G-coupling 4. In thecross-sectional view shown in FIG. 2A, the tapering surfaces of theflange portions 1 e, 3 d each contact the corresponding sloping surfaceof the G-coupling 4 at one point. Actually, each tapering surface andthe corresponding sloping surface make a line contact along the lengthof each semicircular arc portion 4 a shown in FIG. 1B. By fastening thefastener 4 d with the flange portion 1 e of the turbine housing 1 b andthe flange portion 3 d of the bearing housing 3 held between the innersloping surfaces of the G-coupling 4, the turbine housing 1 b and thebearing housing 3 are fastened together. Incidentally, the G-coupling 4is sometimes called a V-band coupling.

As shown in FIGS. 1A and 2A, a heat shield plate 5, which is a thinsheet formed into a tubular shape, is arranged with its edge portionheld between the stopper face of the step portion 1 d of the turbinehousing 1 b and the end face 3 c of the projecting portion 3 b of thebearing housing 3. The heat shield plate 5 is a member for protectingthe bearing housing 3 from high-temperature exhaust gas flowing backwardfrom the turbine housing 1 b. Although this structure itself does notdiffer from that in the prior art as shown in FIG. 2B, the heat shieldplate 5 in the present invention has a greater axial length comparedwith the prior art, which results from setting the axial position of thestopper face of the step portion 1 d nearer to the end face of theflange portion 1 e. When the heat shield plate 5 is to be held betweenthe stopper face of the step portion 1 d of the turbine housing 1 b andthe end face 3 c of the projecting portion 3 b of the bearing housing 3as in the illustrated example, the shape of the projecting portion 3 bneeds to be designed, taking account of the sheet thickness thereof. Itis to be noted that the heat shield plate 5 is not an indispensableelement. In place of the heat shield plate 5, a spacer in the form of athin annular sheet serving as a sealing member may be held between thestopper face and the end face, or the stopper face of the step portion 1d of the turbine housing 1 b may be in direct contact with the end face3 c of the projecting portion 3 b of the bearing housing 3.

Next, a housing fastening method according to an embodiment of thepresent invention will be described in detail. FIG. 3 is an explanatorydiagram indicating sizes referred to in describing a housing fasteningmethod according to an embodiment of the present invention. FIG. 4Ashows a relation between the G-coupling 4 and the flange portions 1 eand 3 d at normal temperature, while FIG. 4B shows a relation betweenthe G-coupling 4 and the flange portions 1 e and 3 d at hightemperature. FIG. 4C shows a relation between gaps Δg and Δc shown inFIG. 4B.

Explanation of symbols relating to sizes in components indicated in FIG.3 is given below:

Pa: Contact position on the turbine housing 1 b against the G-coupling 4Az: Axial distance from the stopper face of the step portion 1 d of theturbine housing 1 b to the contact position PaAr: Radial distance to the contact position Pa on the turbine housing 1b (from the axis Z)Pb: Contact position on the bearing housing 3 against the G-coupling 4Bz: Axial distance from the end face 3 c of the projecting portion 3 bof the bearing housing 3 to the contact position PbBr: Radial distance to the contact position Pb on the bearing housing 3(from the axis Z)θ: Angle of divergence of the G-coupling 4t: Sheet thickness of the heat shield plate 5C: Axial distance between the contact positions Pa and Pb

Explanation of symbols relating to linear coefficients of expansion forcomponents at high temperature and difference in temperature ofcomponents compared with when exposed to normal temperature is givenbelow:

α: Linear coefficient of expansion for the turbine housing 1 b at hightemperatureβ: Linear coefficient of expansion for the bearing housing 3 at hightemperatureγ: Linear coefficient of expansion for the G-coupling 4 at hightemperatureε: Linear coefficient of expansion for the heat shield plate 5 at hightemperatureΔTa: Difference in temperature of the turbine housing 1 b when exposedto high temperature, compared with when exposed to normal temperatureΔTb: Difference in temperature of the bearing housing 3 when exposed tohigh temperature, compared with when exposed to normal temperatureΔTg: Difference in temperature of the G-coupling 4 when exposed to hightemperature, compared with when exposed to normal temperatureΔTs: Difference in temperature of the heat shield plate 5 when exposedto high temperature, compared with when exposed to normal temperature

As shown in FIG. 4A, at normal temperature, the flange portion 1 e ofthe turbine housing 1 b and the flange portion 3 d of the bearinghousing 3 contact the G-coupling 4 at contact positions Pa, Pb,respectively. Generally, between the flange portions 1 e and 3 d, thereexists a slight gap Δp, which is exaggerated in the drawings. Theinventor's research has confirmed that, as shown in FIG. 4B, when theinside of the turbine housing 1 b is exposed to high temperature (ca1000° C., for example), the existence of this gap Δp leads to formationof a gap Δg between the flange portion 3 d of the bearing housing 3 andthe G-coupling 4 due to thermal expansion of the respective components.For example, in the prior art shown in FIG. 2B, when exhaust gassupplied to the turbine 1 is at 1050° C., a gap Δg of 0.0388 mm isformed. Even the gap of such a small size leads to a reduction infastening force applied by the G-coupling 4. Thus, the present inventionneeds to reduce the gap Δg formed when the exhaust gas supplied to theturbine 1 is at 1050° C., at least below the size (=0.0388 mm) in theprior art.

Here, symbol Pg denote a position on the G-coupling 4 which contactedthe contact position Pb at normal temperature. At high temperature, theaxial distance Cg between the contact positions Pa and Pg on theG-coupling 4 is longer than the axial distance C between the contactpositions Pa and Pb on the flange portions 1 e and 3 d. ΔC denotes thisdifference (Cg−C). Regarding ΔC and Δg, a relationship ΔC=Δg/cos(θ/2) isobtained from FIG. 4C. As mentioned above, Δg needs to meet at least thecondition Δg<0.0388 mm. Consequently, ΔC needs to meet the conditionΔC<0.0388/cos(θ/2). For this difference ΔC, an allowable limit k is set.Specifically, in order to achieve at least a slight increase infastening force applied by the G-coupling 4 compared with the prior artwhen the exhaust gas supplied to the turbine 1 is at 1050° C., theallowable limit k needs to be set within the range of0≦k<0.0388/cos(θ/2) (in mm). Further, in the present invention, in orderto effectively keep down the reduction in fastening force applied by theG-coupling 4, the gap Δg should desirably be around 0.002 mm. In thiscase, the allowable limit k should be set within the range of0≦k≦0.002/cos(θ/2) (in mm). When a standard G-coupling 4 is used, therange within which the allowable limit k should be set can be expressedby 0≦k≦0.0016 (in mm).

Using the symbols defined above, the axial distance C between thecontact positions Pa and Pb at high temperature can be expressed by

C={t(1+εΔTs)+Bz(1+βΔTb)}−Az(1+αΔTa)  (1)

On the other hand, the axial distance Cg between the contact positionsPa and Pg at high temperature is expressed by

$\begin{matrix}\begin{matrix}{{Cg} = {{\left( {t + {Bz} - {Az}} \right)\left( {1 + {{\gamma\Delta}\; {Tg}}} \right)} -}} \\{{\begin{Bmatrix}{{{Ar}\left( {1 + {{\alpha\Delta}\; {Ta}}} \right)} -} \\{{\left( {{Ar} + {Br}} \right)\left( {1 + {{\gamma\Delta}\; {Tg}}} \right)} +} \\{{Br}\left( {1 + {{\beta\Delta}\; {Tb}}} \right)}\end{Bmatrix}{\tan \left( {\theta/2} \right)}}}\end{matrix} & (2)\end{matrix}$

Thus, once the allowable limit k is set, the axial distance Az from thestopper face of the step portion 1 d of the turbine housing 1 b to thecontact position Pa and the axial distance Bz from the end face 3 c ofthe projecting portion 3 c of the bearing housing 3 to the contactposition Pb can be determined to meet the relationship

0≦ΔC≦k  (3)

In other words, in the present embodiment, by using the aboveexpressions (1), (2) and (3), the values of the parameters (axialdistance Bz, radial distance Br, angle of divergence θ, etc.) relatingto the shape of the projecting portion 3 b can be determined takingaccount of the sheet thickness t (thickness of the thin sheet), andtherefore the shape of the projecting portion 3 b can be designed takingaccount of the sheet thickness t.

By determining the axial distance Az in the recessed portion and theaxial distance Bz in the projecting portion according to theabove-described housing fastening method, reduction in fastening forceapplied by the G-coupling 4 can be kept down, irrespective of the modelor capacity of the turbocharger. This method is applicable to productsother than turbochargers (waste gate valves, exhaust manifolds andmufflers, for example) having housings to be fastened by a G-coupling 4.

Next, referring to FIGS. 5A and 5B, housing fastening methods accordingto other embodiments of the present invention will be described. FIG. 5Ais a longitudinal cross-sectional view showing a fastening structuremade by a housing fastening method according to another embodiment ofthe present invention, and FIG. 5B is a longitudinal cross-sectionalview showing a fastening structure according to a further embodiment.The components similar to those shown in FIG. 2A are assigned the samereference characters, and the explanation of such components is omittedto avoid repetition.

In the embodiment shown in FIG. 5A, the flange portion 3 d of thebearing housing 3 is Ah greater in outside diameter (radius) than theflange portion 1 e of the turbine housing 1 b. This is out ofconsideration for the fact that the turbine housing 1 b is likely toexperience a greater temperature rise and therefore a greater degree ofthermal expansion than the bearing housing 3. In other words,considering that the difference in thermal expansion results indifference in radial displacement between contact positions Pa and Pb,the configuration is determined such that, at high temperature, thecontact positions Pa and Pb are displaced onto a line approximatelyparallel to the axial direction. To this case, the above-mentionedexpressions for calculating the axial distance C between contactpositions Pa and Pb and the axial distance Cg between contact positionsPa and Pg can be applied without modification. It is to be noted,however, that even when the housing fastening method shown in FIG. 5A isnot adopted, the axial distance C between contact positions Pa and Pbcan be easily calculated taking account of an angle between a lineconnecting the contact positions Pa and Pb and the axial direction.

In the embodiment shown in FIG. 5B, the stopper face of the step portion1 d of the recessed portion 1 c of the turbine housing 1 b is in directcontact with the end face 3 c of the projecting portion 3 b of thebearing housing 3. In other words, this is the case not requiring a heatshield plate 5 as shown in FIG. 2A. This is presented considering thefact that some models of turbocharger do not require a heat shield plate5. In this case, the axial distances C and Cg can be easily calculatedonly by eliminating the variables relating to the heat shield plate 5(t, ε, ΔTs) from the above-mentioned expressions for calculating theaxial distance C between contact positions Pa and Pb and the axialdistance Cg between contact positions Pa and Pg, respectively. Further,in the case where a spacer or a sealing member is provided between thestopper face of the step portion 1 d and the end face 3 c of theprojecting portion 3 b in place of the heat shield plate 5, the axialdistances C, Cg can be calculated by introducing the sheet thickness andliner coefficient of expansion for such member.

The present invention is not limited to the above-described embodiments.Needless to say, it allows a variety of modifications not departing fromthe spirit and scope of the present invention. For example, the presentinvention is applicable to fasteners other than the G-coupling.

1. A housing fastening method comprising steps of inserting a projectingportion of a housing in a recessed portion of another housing so that anend face of the projecting position butts against a step portion of therecessed portion serving as a stopper face and that a flange portionaround the recessed portion and a flange portion around the projectingportion face each other, and thereafter, fastening the flange portionstogether by an annular fastener with a grooved portion on its insideadapted to receive the flange portions facing each other, wherein theaxial position of the stopper face of the step portion and the shapes ofthe recessed portion and the projecting portion are determined to ensurethat a gap produced between the grooved portion of the fastener and theflange portions does not exceed a specified size even when the housingsand the fastener experience thermal expansion during use.
 2. The housingfastener method according to claim 1, wherein the axial position of thestopper face of the step portion is set within the axial projected widthof the fastener.
 3. The housing fastening method according to claim 1,wherein the shape of the projecting portion is determined taking accountof the thickness of a thin sheet held between the stopper face of thestep portion and the end face of the projecting portion.
 4. The housingfastening method according to claim 1, wherein when the housings arelikely to experience different degrees of thermal expansion during use,the flange portion of the housing which is likely to experience asmaller degree of thermal expansion is formed to be greater in outsidediameter than the flange portion of the housing which is likely toexperience a greater degree of thermal expansion.
 5. The housingfastening method according to claim 1, wherein an axial distance Az froma contact position at which the fastener contacts the flange portionaround the recess portion to the stopper face of the step portion and anaxial distance Bz from a contact position at which the fastener contactsthe flange portion around the projecting portion to the end face of theprojecting portions are determined to meet the condition0≦Cg−C≦allowable limit k, where C is an axial distance between thecontact positions on the flange portions defined by an expressionC=t+Bz−Az, on the basis of said axial distances Az and Bz, and Cg is anaxial distance between the contact positions on the fastener.
 6. Thehousing fastening method according to claim 5, wherein the allowablelimit k is set on the basis of the allowable size for a gap producedbetween the fastener and the contact position on the flange portion at aspecified temperature.
 7. The housing fastening method according toclaim 5, wherein the allowable limit k is set to meet the condition0≦k<0.0388/cos(θ/2), where θ is an angle of divergence of a pair ofsupport portions of the fastener.
 8. A turbocharger comprising a turbineincluding a bladed rotor rotated by a fluid supplied thereto, acompressor including an impeller for drawing in air, connected with thebladed rotor by a rotating shaft, a turbine housing constituting anouter shape of the turbine, and a bearing housing rotatably supportingthe rotating shaft, a projecting portion of the bearing housing beinginserted in a recessed portion of the turbine housing such that an endface of the projecting position butts against a step portion of therecessed portion serving as a stopper face and that a flange portionaround the recessed portion and a flange portion around the projectingportion face each other, the flange portions being fastened together byan annular fastener with a grooved portion on its inside adapted toreceive the flange portions facing each other, wherein the bearinghousing and the turbine housing are fastened together by the fastener byemploying the housing fastening method according to claim 1.